Basilar thumb arthritis (arthritis at the base of the thumb) of the carpo-metacarpal (CMC) joint is thought to be the most common arthritis of the homosapien. It typically presents as a symptomatic problem in the sixth decade of life and its incidence increases thereafter. It is a result of the rather recent phylogenetic appearance of a highly mobile, strong thumb ray. The thumb acts as the pivotal and guiding member of the defining anatomical features of the human, the prehensile hand. The brain's cortical representation area of the thumb is huge. The thumb allows for a panoply of activities from watch making to weightlifting. Unfortunately, this distinct anatomical advantage can result in arthritis of the CMC joint of the thumb.
It is believed that gaming and cell phone text-messaging and the like may also lead to basilar thumb arthritis, with a resulting increase in incidence as well as a potential earlier onset that has been conventional.
Anatomically, the CMC joint includes the trapezium articulating with the base of the first metacarpal as shown in FIG. 1. As shown in FIG. 2, the CMC joint is a saddle joint allowing abduction toward the palm, abduction away from the palm, opposition (toward the 5th finger), and extension or retroposition (backward or hitch-hiker position.) As shown in FIG. 3B, the articular surface of the base of the 1st metacarpal 20 is divided into dorsal and palmer slopes and a central saddle portion. As shown in FIG. 3A, the opposing articular surface of the trapezium 10 also has two parts: a spherical portion 11, which articulates with the slopes of the first metacarpal; and a saddle portion 12, which articulates with the saddle portion of the 1st metacarpal. (See, e.g., Zancolli et al., Biomechanics of the trapezio-metacarpal joint, Clinical Orthopaedics and Related Research, No. 220, July 1987, pp. 14-26). FIG. 3C illustrates an enlarged “normal” or “natural” trapezium 10 and first metacarpal base 20b. 
The subchondral (below cartilage) bone of the trapezium-first metacarpal is covered by hyaline cartilage. This cartilage is typically the first tissue to deteriorate during arthritic wear of the joint. Initially, thinning and pitting occurs, which can be followed by osteophyte (bone spur) formation and subluxation (loss of congruity) of the joint.
Over the past fifty years various arthroplasties have been proposed to try to alleviate the disabling pain of CMC arthritis. Generally stated, the arthroplasties have been either soft tissue interpositions, implant interpositions, or partial joint replacements using implants. The implant procedures either have replaced the base of the first metacarpal or replaced the trapezium following trapezectomy.
Currently, 1st metacarpal implants involve inserting an intramedullary stem into the base of the 1st metacarpal, to which is attached a convex articular surface replacement. Trapezial implants generally have the shape of the anatomic trapezium. In both cases, an implant material (e.g., metal, silicone, or ceramic) articulates with a bone surface where motion occurs. These procedures do not attempt to replace the joint but rather act as spacers. Fortunately, they can reduce the arthritic pain, but problems have arisen. Potential problems include implant loosening, implant breakage, implant dislocation, adverse tissue reaction to the implant (particularly silicone), failure of pain relief, loss of strength, and implant subsidence (sinking in or erosion of the residual trapezium, as in 1st metacarpal implants). It is believed that because of these problems, the most common procedure currently performed for CMC arthritis is a soft tissue interposition suspension procedure also known as “ligament reconstruction with tendon interposition (LRTI)” where no implant is used.
In view of the foregoing, there remains a need for alternative thumb CMC implants.